Polyethylene terephthalate (PET) which has excellent mechanical characteristics, chemical resistance, etc. is used for molded containers, film labels and the like. Particularly in recent years, containers made of PET are widely used for beverage bottles, which are called PET bottles. Along with a drastic increase in the amount of use of the PET bottles, from the viewpoint of the recent environmental problems and resource saving, a movement of recovering used PET bottles and recycling them as a resource is actively carried out. For example, Japanese Patent Laid-Open 2000-282326 discloses an invention of forming recyclable polyester resin products represented by PET bottles into filaments, which are used as fiber products for clothes and for industrial materials.
A PET bottle is wrapped with a film label to exhibit the name of the article, the contents, etc. Since the bottle has to be wrapped in accordance with its three-dimensional shape, usually a heat-shrinkable film label is used. Heretofore, as heat-shrinkable films, drawn films such as polyvinyl chloride films and polystyrene films have been widely used, and in recent years, polyester films have been greatly expected, and the amount of their use is increasing along with the increase in the amount of use of PET bottles.
Therefore, production of heat-shrinkable polyester film labels from recycled PET bottles has been considered, since the cost of the labels will be reduced, and recycling of PET bottles will be achieved. However, a recycled material obtained from the recycled PET bottles is a random mixture of various PET and physical properties such as melt viscosity and molecular weight vary greatly. Accordingly, in production of heat-shrinkable polyester films, if PET bottle-recycled materials are used in an amount of about 45 mass % for example, molecular weight and the like are reduced due to repeated use of PET, whereby the resulting films have low mechanical strength, heat resistance, etc. Further, in film formation of polyester films, it is required to carry out melt extrusion, to rapidly cool the extruded product while it is electrostatically contacted on a casting roll to obtain an undrawn film, and to draw the film in a longitudinal direction and/or in a transverse direction to develop heat shrinkage properties. However, a film using the PET bottle-recycled material in a large amount tends to be inferior in the electrostatic adhesion properties to films obtained from non-recycled PET, whereby the film formation rate is not so high as that of usual films, thus impairing the productivity.